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3.4. Overvoltage protection

In some cases, the power supplies are equipped with a circuit whose mission is to prevent the power supply, as a consequence of a malfunction or fault, from supplying the load with a voltage much higher than the normal value. This circuit usually consists of a thyristor which short-circuits the output when an auxiliary circuit detects an overvoltage condition. This system is called crowbar circuit (fig. 17). When the output has a relatively higher current, it is more usual to act upon the power supply control, avoiding the use of large and costly thyristors.